Radio receiving system



V. BUSH.

RADIO RECEIVING SYSTEM.

APPLICATION FILED MAY I9, I920.

1,389,026. Patented Aug. 30, 1921.

Ram??? TED STATES PATENT OFFIQE.

VANNEVAR BUSH, OF CHELSEA, MASSACHUSETTS, ASSIGNOR TO AMERICAN RADIO 8:; RESEARCH CORPORATION, OF MEDFORD, MASSAGKUSETTS, A. CORPORATION 01 DELAWARE.

Specification of Letters Patent.

Patented Aug. 30, 1921.

Application filed May 19, 1920. Serial No. 382,672.

To all whom it may concern.-

Be it known that I, VANNEVAR BUSH, a citizen of the United States, residing at Chelsea, in the county of Suffolk and State of Massachusetts, have invented certain new and useful Improvements in Radio Receiving Systems; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The present invention relates to receiving circuits more particularly adapted for receiving sustained oscillations at radio frequency. It is 'desirable to provide receiving circuits which will break up or modulate sustained oscillations into groups at audible frequency so that an audible tone may be produced in a telephone receiver.

The object of the present invention is to provide a simple and effective form of circuit for transforming sustained oscillations into groups at audible frequency. This object is attained in the present invention by periodically varying the resistance of the receiving circuit at audible frequency in such a manner that the sustained oscillations are correspondingly absorbed and groups of oscillations at audible frequency pass through the receiving apparatus.

This may be conveniently accomplished by introducing into the receiving circuit a rectifier and a source of nonuniform current to cause the circuit containing the rectifier to become periodically active and inactive at audible frequency. When current is flowing through the rectifier .the absorbing circuit containing the rectifier is out of tune with the remainder of the receiving circuit and in consequence does not affect the received oscillations. During the period when no current is flowing through the rectifier, however, the oscillations set up in the absorbing circuit are suflicient to absorb the entire energy from the antenna circuit and prevent the receiver from operating.

In the simplest and most eflicient form of the invention which has yet been devised a crystal detector is employed in conjunction with a source of alternating current, both be? is especially desirable as the change from a ing included in an absorblng circuit induc tively coupled to the antenna circuit in such a manner that when current is flowing through the crystal detector the received oscillations are not affected but during the period when no current is flowing through the detector the oscillations of the absorbing circuit completely absorb the oscillations of the antenna circuit, preventing the operation of the receiver. As the resistance of this crystal detector changes gradually the current in the telephone receiver is approximately sinusoidal, causing a clear musical note in the telephone.

The accompanying drawing illustrates a receiving circuit embodying one specific application of the present invention.

In the specific embodiment of the invention shown in the drawing, a usual antenna circuit 10 is shown inductively coupled with a telephone receiving circuit 11 through a transformer indicated at 12. The telephone receiving circuit shown includes the usual telephones 14 connected across a condenser 16, a crystal detector 17 and condenser 18.

In order to periodically absorb the'oscillations of the antenna circuit at audible frequency, an absorbing circuit 19 is shown as inductively coupled at 20 to the antenna circuit. This absorbing circuit includes a crystal rectifier indicated at 21 connected in parallel with a condenser 22. A. convenient source of alternating current at audible frequency is provided through a battery 24 and buzzer 25. As will be obvious to those skilled in the art, this alternating current is rectified by the crystal 21, causing a periodic flow of current therethrough at audible frequency. During the period at which current is flowing through the rectifier, the associated condenser 22 is practically short circuited and the circuit thus formed is out of tune with the received oscillations. During the period, however, in which no current is flowing through the crystal 21, the oscillations set up in the absorbing circuit 19 absorb suflicient energy from the antenna circuit to prevent the receiver from operating. Thus the received oscillations are broken up into groups at audible frequency and a note is produced in the telephones 14. The absorbing circuit is provided with choke coils 29 and 30 which preventthe buzzer from exciting the radio fre uency-circuit by impact.

1 T e use of a crystal in the absorbing circuit conducting. medium to a non-conducting medium occurs gradually, the resistance being dependent upon the current flow. This gradual change causes a correspondingly gradual change of resistance in the receiving circuit and the production of a musical tone in the tele hone receivers.

It shoul be understood that various forms of rectifier media other than that shown may be employed in the absorbing circuit and that this circuit may be connected into the receiving circuit in a variety of ways. Furthermore the receiving circuit may employ an one of the usual oscillation detectors whic will be periodically rendered active.

I claim- 1. The combination in a radio receiving circuit having a detector of a resistance which is periodically rendered conducting and non-conducting, and circuit connections for causing the received oscillations to be periodically absorbed without passing through the detector.

2. The combination in a radio receiving circuit having a detector of a source of nonuniform current varying at audible frequency and a rectifier through which the current is passed with accompanying circuit connections for rendering the receiving circuit periodically inoperatlve at audible frequency.

3. A radio receiving circuit comprising an oscillation detector, a crystal rectifier, a source of alternating current at audible frequency connected with the rectifier, and circuit connections for causing the received oscillations to be periodically absorbed by the circuit containing the rectifier without passing through the oscillation detector.

4-. A radio receiving circuit comprising an oscillation detector, an absorbing circuit including a rectifier, a source of alternating current at audible frequency and a condenser shunted across the rectifier, and circuit connections for causin the received osclllatlons to be periodical absorbed in the absorbing circuit wit out passing through the oscillation detector.

5. radio receiving circuit comprising an antenna circuit, a telephone receiv'in c1rcu1t inductivel coupled therewith an including an oscil ation detector and an absorbmg circuit inductively coupled with the antenna circuit and including a source of alternating current at audible frequency and a rectifier, the absorbing circuit being adapted to perlodically absorb the received 05- cillations of the antenna circuit during the periods when the rectifier is non-conducting.

6. A radio receiving circuit comprising an antenna circuit, a telephone receiving clrcuit inductively coupled therewith and including an oscillation detector and! an absorbing circuit including a rectifier and a source of non-uniform current adapted to render the rectifier periodically conducting and non-conducting, means for tuning the absorbin clrcuit to cause the latter to completely a sorb the oscillations in the antenna circuit during a period when the rectifier is rendered non-conducting.

7. A radio receiving circuit comprising an oscillation detector, a circuit including. the detector, a separate absorbing circuit including a crystal rectifier and a source of non-uniform current at audible frequency to render the rectifier periodically conducting and non-conducting at a like frequency, and associated means in the absorbing circuit for absorbing the oscillations in the antenna circuit during the period when the rectifier is non-conducting to periodically render the oscillation detector inactive.

VANNEVAR BUSH. 

